Selective hydrogenation



United States Patent 3,203,998 SELECTIVE HYDROGENATION William Thomas House, Baton Rouge, La., and Rhea N. Watts, deceased, late of St. Francisville, La., by Beulah Smith Watts, legal representative and sole heir, St. Francisville, La., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Feb. 6, 1963, Ser. No. 257,365 8 Claims. (Cl. 260-617) The present invention relates to an improved process for the hydrogenation of oxygenated compounds and is a continuation in part of SN. 94,641, filed March 9, 1961, now abandoned. More specifically this invention relates to the selective hydrogenolysis of secondary alcohols from a mixture of alcohols to form paraflins in the presence of particular catalysts at temperatures in the range of 450 to 550 F., at hydrogen pressures in the range of 1000 to 4000 p.s.i.g. In one embodiment this invention relates to selectively hydrogenolyzing secondary alcohols to parafiins in the presence of primary alcohols using a molybdenum sulfide catalyst. In another embodiment this invention relates to selectively hydrogenolyzing a secondary alcohol group from a single molecule containing both primary and secondary alcohol groups using a molybdenum sulfide catalyst. In one preferred embodiment the concept of this invention may be applied to selectively hydrogenolyze, in the presence of molybdenum sulfide catalyst, a mixture of alcohols obtained from telomerizing methanol with ethylene to thus remove the secondary alcohols obtained in the process. By this latter process a pure primary alcohol is obtained. In another preferred embodiment a mixture of oxygenated products obtained, for example, from the air oxidation of paraifins is hydrogenated and selectively hydrogenolyzed, in the presence of a molybdenum sulfide catalyst, to yield a mixture of primary alcohols and parafi'lns.

Prior to the present invention the selective hydrogenolysis of secondary saturated alcohols form a mixture of saturated alcohols to parafiins was practically unknown in the art. Thus according to most text books such a hydrogenolysis was believed to be feasible only when labilizing groups (i.e. carbon-carbon unsaturation, carbonyl groups or hydroxyl groups) were adjacent to the hydroxyl function, and not at all with materials not containing these labilizing groups. The only known hydrogenation of these latter materials to paraifins is described in an article in Chem. Listy, volume 50, pages 569-572 (1956). In this article the hydrogenolysis of tertiary, secondary and primary alcohols is disclosed, all obtained with about the same selectivity under similar conditions. No mention of selective hydrogenolysis of secondary alcohols admixed with primary alcohols was disclosed.

It has now been surprisingly discovered that secondary alcohols may be selectively hydrogenolyzed in the pres ence of primary alcohols, without any substantial losses of primary alcohols, by utilizing specifically a molybdenum sulfide catalyst. This process is particularly attractive for use in processes wherein synthetic alcohols are produced by telomerization. In this process the product comprises a mixture of primary and secondary alcohols which vary in chain length from a few carbon atoms to 25 carbon atoms, together with smaller amounts of hydrocarbons. The valuable products are of course the primary alcohols. Since the separation of primary from secondary alcohols by distillation, solvent extraction or other known means is extremely difiicult because of the overlapping of boiling points and solubilities of the components of the telomer product, this process is particularly advantageous.

The alcohols which may be hydrogenolyzed according ice to the present process are mixtures of C -C primary and C -C secondary saturated monoalcohols. These alcohols include both straight and branched chain alcohols and additionally include cyclic alcohols. Examples of these alcohols are methanol, ethanol, normal propanol, isopropanol, normal butanol, isobutanol, the appropriate pentanols, heptanols, hexanols, octanols, nonanols, decanols, hendecanols, dodecanols, tridecanols, eicosonols, etc. Examples of the cyclic saturated alcohols are cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, cycloeic'osonol, etc. The invention may be applied to treat specific alcohols of these classes or mixtures of these alcohols. Since somewhat different conditions are used depending upon the molecular weight of the alcohols to behydrogenolyzed, higher selectivities in the hydrogenolysis of secondary alcohols from primary alcohols are obtained where the primary and secondary alcohols are of similar molecular weight. In addition, the hydrogenolysis may be applied to polyols containing mixtures of primary and secondary alcohol groups on a single molecule. Typical examples of glycols which may be utilized in carrying out the process are C to C glycols such as l,3-hexanediol and C to C alkyl substituted glycols such as 2-ethy1-1,3-hexanediol.

Where tertiary alcohols are present with the primary and secondary alcohols, these alcohols will also be hydrogenolyzed by the present process. Thus, the tertiary alcohols will be hydrogenolyzed to parafiins and can thus be easily removed from the desired alcohols, i.e. the primary alcohols with the other parafiins formed. These tertiary alcohols again may be C -C branched saturated monoalcohols corresponding to those described above.

Particularly attractive feed stocks for hydrogenolysis are the telomer alcohol products obtained by telomerizing methanol with a C -C olefin, preferably ethylene, in the presence of a free radical initiator. Processes for preparing these alcohols are described, for example, in US. 2,668,181. Additionally other methods for preparing telomer alcohol may be utilized to prepare an alcohol feed stock for the present process. Typical compositions of telomer product alcohols may be C C alcohols, containing 15-50 weight percent, e.g. 25 wt. percent secondary alcohols, 1-5 wt. percent e.g. 2 wt. percent tertiary alcohols, 1025 wt. percent e.g. 15 wt. percent hydrocarbon.

The concept of this invention has also been found to be of particular value in the hydrogenation of parafiin oxidation products yielding a predominance of primary alcohols upon the selection of a suitable catalyst in ac cordance with this invention. Thus, the hydrogenation of paraflin oxidation products with a molybdenum sulfide catalyst not only produces the corresponding alcohols of said oxidation products but also selectively and continuously hydrogen'olyzes the secondary alcohols to yield parafi'ins. The mixture of primary alcohols and paraflins may then be separated by conventional methods and the paraffins recycled to the oxidation stage. The concept of this invention therefore provides an economical route for the preparation of straight chain primary alcohols which are extremely valuable as intermediates in the production of plasticizers and detergents.

The paraffin oxidation products utilized in conjunction with this invention may be obtained by any of the well known techniques for oxidation of parafiinic petroleum fractions such as crude scale Wax and petrolatum. Hence, both catalytic and non-catalytic oxidation processes may be successfully employed. Suitable catalysts for the air oxidation include aqueous KMnO cobalt soaps and manganese soaps. In a less preferred embodiment boric acid may also be present to obtain higher selectivities to alcohols at the expense of lower selectivities to primary rather than secondary alcohols. Oxidation temperatures may vary from 200 to 400 F. and preferably 240 to 300 F. Suitable processes for oxidation of parafiins are described, for example, in US. Patent 2,121,367.

The normal oxidation sequence of paratfins is known to begin by a free radical attack at random at all secondary carbon atoms of the normal parafiin. The primary oxidation products of this reaction are ketones. One mole of water is also formed per mol of paraffin reacting. Acids are also formed by chain cleavage at positions adjacent to the keto group. Several secondary reactions in the oxidation sequence cause the formation of secondary alcohols and lactones. Thus the typical paraffin oxidation product consists of ketones, acids, secondary alcohols and lactones.

The catalysts used in the present hydrogenolysis process are sufides of molybdenum.

These catalysts may of course be supported on inert carriers of any of the readily available types. Thus, examples of carrier materials which may be used as solid support components of the catalysts are the various alumi- A preferred sulfided cobalt molybdate catalyst has the following general composition: 1-5 wt. percent, preferably 2-4 wt. percent colbalt oxide and 5-15 wt. percent, preferably 8l2 wt. percent molybdenum oxide on a carrier of the type above described, e.g. activated carbon, sulfided to saturation with H 8.

Using this procedure a complete process for obtaining secondary alcohols from paraflins may be obtained by carrying out the first step air oxidation under the conditions described above, also in the presence of boric acid which directs the oxidation to obtain high selectivities to secondary alcohols.

The present invention will be more clearly understood from a consideration of the following examples.

EXAMPLE 1 The following feed compositions were hydrogenated in a 2000 cc. stainless steel bomb in the presence of catalysts shown, under the conditions described in the following table. The amount of the catalyst used in all runs was 50 volume percent total catalyst based on the alcohol supplied.

Table I BOMB HYDRO GENATION OF SYNTHETIC TELOMER ALCOHOLS Percent alcohol destroyed Holding (analyzed by gas chroma- Feed, vol. percent in Temp., time, Hydrogenation Hg pres, tography) octanol-l F. hrs. 1 catalyst p.s.1.g.

Primary Secondary 10% Octauol-2 500 6 3, 000 15. 5 100 Do 525 6 3, 000 19.0 100 500 3 3, 000 5. 6 100 475 6 3,000 11. 5 83. 0 500 12 3, 000 31. 0 100 475 12 3, 000 16. 0 86. 0 500 1 3, 000 1. 9 59. 0 500 1 3, 000 2. 2 55. 0 500 2 3, 000 1. 3 e9. 0 500 2 1, 000 1. 3 64. 0 500 1 3, 000 3. 5 l7. 0 500 2 S-Co molyb- 3, 000 63. 2 22. 0

date 500 2 Cu Chromite 3,000 0 0 500 2 S-l0 5 3, 000 4. 6 46 500 2 S-Ni Tungsten 3, 000 31. 7 100 Do 500 4 MoSz 7 1, 000-2, 000 14. 5 67 Octanol-2 in dodecanol. 500 2 S-dCotLgolyb- 3, 000 77 60 1 After 3 hours heat-up time.

2 9% M003 on activated carbon sulfided with H28.

3 2% Co0+10% M003 on activated carbon sulfided with His.

4 Copper chromite (unsupported copper chromite).

5 Equimolar mixture of ZnO, MgO and M003 sulfided with H s.

5 90% NIS+10% W8 7 P.s.i.g. increased with time after heat-up time.

nous and silicious materials of natural or synthetic origin such as bauxite, aluminum oxide, activated alumina, kieselguhr, magnesium oxide, magnesium silicate, magnesium carbonate, barium sulphate, pumice, kaolin, activated carbon, clays, carborundum, alundum, and the like. These catalysts preferably contain 5-25 wt. percent of the active material supported on a carrier of the type above described, e.g. activated carbon. A preferred molybdenum sulfide catalyst has the following general composition: 5-15 wt. percent, preferably 810 wt. percent, e.g. 9 wt. percent molybdenum oxide on a carrier of the type above described, e.g. activated carbon, sulfided to saturation with H S.

Reaction conditions for the present process are as follows: Temperature, 400-600 F., preferably 450550 F., e.-g. 500 F.; hydrogen pressure, 500-4000 p.s.i.g., preferably 2500-3500 p.s.i.g., e.g. 3000 p.s.i.g., holding times, l-l5 hours, preferably 1-12 hours, e.g. 3 hours. The amount of the catalyst utilized is 1-16 volume percent, preferably 5-25 volume percent, e.g. 10 volume percent based on the total alcohol supplied.

In a less preferred embodiment primary alcohols may be selectively hydrogenated from secondary alcohols by use of a sulfided cobalt molybdate catalyst under the conditions described above.

EXAMPLE 2 Heptanol-3 /heptanol-l ratio: 1

Feed 0.48

Product 0.0

'Considered to be a measure of secondary to primary alcohol ratio.

EXAMPLE 3 Cetane, a C paraffin feed, was added to a one gallon stirred autoclave and air oxidized under the following conditions:

Catalyst Mn soap Wt. percent 0.05 Mn Temp. F. 275 Air rate, liters/ hr./ gm "'30 Time, hrs. 11-12 ,5. The resulting oxygenated products were analyzed for functional groups by KOH numbers. The KOH numbers are defined as follows: Hydroxyl No. is the mg.

6 tional groups by KOH numbers both before and after hydrogenation.

The results are summarized below:

KOH equivalent to acid necessary to esterify 1 g. of material; acid No. is mg. KOH required to neutralize 1 g. of material; ester No. is mg. KOH required to saponify 1 g. of material.

The results are as follows:

Hydroxyl No. 30 Acid No. 125 Ester No. 124

API gravity 23.2

The total oxidation product was hydrogenated in a shaker autoclave in the presence of 50 vol. percent, based on oxidation product feed, of the molybdenum sulfide catalyst of Example 1. The reaction was carried out at 475 F. and a pressure of 3000 p.s.i.g. for a period of 12 hrs. Analysis for functional groups based on KOH numbers resulted as follows:

Hydroxyl No. 148 Acid No. 3.7 Ester No. 59 API gravity 37.2

Percent Alcohols (Cg-C14) 46 Cetane 35 Heavy products 19 Each alcohol present i113 to 4% concentration.

This distribution corresponds to approximately 70% selectivity to alcohols, the main non-selective components being the 19% heavy products.

EXAMPLE 4 A cetane feed was oxidized in several runs utilizing different catalysts and temperatures. The catalysts for the several runs were aqueous KMnO manganese soaps and cobalt soaps. Temperatures in the range of 240 to 300 F. were utilized. The oxidation product from each run was distilled and separated into a light acid fraction, a heavy acid fraction, a bottoms fraction and an unreacted feed fraction. The similar fractions from each oxidation run were then contemplated.

The composited light acid fraction and the composited combined heavy acid and bottoms fraction were hydrogenated in the presence of the molybdenum sulfide catalyst and in accordance with the procedure of Example 3 above. Both fractions were analyzed for func- The cleanup of acids and esters by hydrogenation of the light acid fraction is essentially complete. It is somewhat less complete in hydrogenation of the heavy acids including distillation bottoms. From KOH balances calculated for the above hydrogenations selectivity of the hydrogenation for yielding primary alcohols may be demonstrated.

Overall KOH balance, percent Hydrogenation feed Primary KOH balance, percent Light acids Heavy acids and bottoms The overall KOH balance is defined by the relationship 35 to 55% of the functional groups during hydrogenation. These are the groups that the molybdenum sulfide catalyst hydrogenated to paraflins, e.g. keto and secondary OH groups. The oxidation of paraflins has been theorized to involve a free radical attack on the hydrocarbon chain and thus the alcohols formed during oxidation would be secondary alcohols. The primary KOH balances have been calculated on the assumption that the OH number of the hydrogenation feed represents all secondary functions and the CO number represents all keto functions. The near 100% primary KOH balance indicates that the above assumptions are correct and that the alcohols obtained as hydrogenation product are primary alcohols obtained from the hydrogenation of the acids and esters. The 78% primary KOH balance for hydrogenation of the heavy acids plus bottoms indicates that some functionality other than that represented by the hydroxyl and carbonyl numbers of the feed is lost during hydrogenation. This is undoubtedly the secondary OH groups associated with lactones which show up as esters in the feed.

These calculations illustrate very strikingly the selective scavenging action of the hydrogenation catalyst for keto, secondary hydroxyl and lactone groups.

EXAMPLE 5 A feed consisting of 2 ethyl-1,3-hexanediol was hydrogenated in a bomb at a temperature of 500 F. and a hydrogen pressure of 3000 p.s.i.g. in the presence of 50 vol. percent based on feed, of the molybdenum sulfide catalyst of Example 1. The following results were period of 1 to hours and recovering a mixture of products consisting essentially of primary alcohols and paraf The remaining products after the above described hydrogenolysis were paraflins.

EXAMPLE 6 A C C alcohol fraction representing about 55 volume percent of the crude, cetane-free product from hydrogenation of the light acid fraction of Example 4 was obtained by vacuum distillation. This alcohol represented an average carbon number of 7.6, was water-white, and had an odor very similar to normal octanol. The infrared spectrum was virtually identical to normal octanol except for a small absorption in the carbonyl (ester) region. No evidence for the presence of secondary alcohols was detected.

This alcohol fraction was esterified with phthalic anhydride using an excess of the anhydride because it was desired to convert all alcohols to esters and recover any non-alcohol impurities for further study. The rather severe esterification and stripping conditions (to remove phthalic anhydride) gave a medium yellow ester. Optimum esterification conditions and normal decolorization procedures should give good color esters. An infrared trace on the recovered esters was essentially identical to a reference spectrum for normal octyl to normal decyl phthalate, except for trace absorption attributed to residual phthalic anhydride. The recovered strippings indicated the original fraction contained about 12% nonalcohol impurities, mainly light esters and hydrocarbons. Preliminary plasticizer evaluations on these esters indicate that their properties are generally comparable to those of diisooctyl phthalate and di-Z-ethylhexyl phthalate, which are obtained by esterification of linear primary alcohols.

The above tests indicate that hydrogenolysis with a molybdenum sulfide catalyst selectively yields a primary straight chain alcohol from a mixture containing both primary and secondary functional groups.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations, and that modifications may be made without departing from the spirit of this invention.

What is claimed is:

1. A process for selectively hydrogenating a mixture of C to C primary monohydric alcohols and C to C secondary monohydric alcohols which comprises contacting a mixture with hydrogen in the presence of 1 to 60 volume percent, based on said alcohols, of a molybdenum catalyst at a pressure in the range of 1,000 to 4,000 p.s.i.g. and a temperature in the range of 400 to 600 F. for a 2. The process of claim 1 where the alcohol feed comprises C to C tertiary alcohols in addition to said primary and secondary alcohols.

3. The process of claim 1 wherein said mixture of alcohols is obtained from the telomerization of methanol with ethylene and contains 15-50 wt. percent of secondary alcohols, l-5 wt. percent of tertiary alcohols, 10-25 wt. percent hydrocarbons, the remainder being primary alcohols.

4. The process of claim 1 in which the catalyst is a 5-15 wt. percent molybdenum oxide on an inert support catalyst sulfided to saturation with H S.

5. The process of claim 4 in which the catalyst is supported on activated carbon.

6. The process of claim 4 wherein said mixture of oxygenated compounds is obtained by the oxidation of paraffinic petroleum fractions.

7. A process for producing C to C primary alcohols by selective hydrogenation of a paraflin oxidation product. which comprises contacting said paraflin oxidation product obtained by air oxidation of a paraffin in the presence of a catalyst selected from the group consisting of aqueous KMnO cobalt soaps and manganese soaps at temperatures in the range of 200 to 400 F., with hydrogen in the presence of 1 to volume percent based on total alcohols in said parafiin oxidation product of a molybdenum sulfide catalyst at a pressure in the range of 1000 to 4000 p.s.i.g. and a temperature in the range of 400 to 600 F. for a period of 1 to 15 hours and recovering a mixture of products consisting essentially of primary alcohols and parafiins, separating said mixture of alcohols and parafiins and recycling said parafiins to said air oxidation step.

8. A process for selectively hydrogenating a C to C polyol containing both primary and secondary hydroxyl groups in a single molecule which comprises contacting said polyol with hydrogen in thepresence of 1 to 60 volume percent, based on said polyol, of a molybdenum catalyst at a pressure of 1,000 to 4,000 p.s.i.g. and a temperature in the range of 400 to 600 F. for a period of 1 to 15 hours and recovering a primary alcohol.

References Cited by the Examiner Moldavski et al.: Chem. Abstracts, vol. 29 (1935), p. 2153.

JOSEPH R. LIBERMAN, Primary Examiner.

LEON ZITVER, Examiner. 

1. A PROCESS FOR SELECTIVELY HYDROGENATING A MIXTURE OF C1 TO C30 PRIMARY MONOHYDRIC ALCOHOLS AND C3 TO C30 SECONDARY MONOHYDRIC ALCOHOLS WHICH COMPRISES CONTACTING A MIXTURE WITH HYDROGEN IN THE PRESENCE OF 1 TO 60 VOLUME PERCENT, BASED ON SAID ALCOHOLS, OF A MOLYBDENUM CATALYST AT A PRESSURE IN THE RANGE OF 1,000 TO 4,000P.S.I.G. AND A TEMPERATURE IN THE RANGE OF 400 TO 600* F. FOR A PERIOD OF 1 TO 15 HOURS AND RECOVERING A MIXTURE OF PRODUCTS CONSISTING ESSENTIALLY OF PRIMARY ALCOHOLS AND PARAFFINS. 